The invention relates to the preparation of aluminoxanes by addition of water to a solution of trialkylaluminum in an inert solvent, the water required for the reaction being metered via a mixing nozzle into a static mixer, in particular a jet loop reactor.
Longer-chain oligomeric and/or polymeric alkylaluminoxanes of the simplified structures ##STR1## are known compounds, which are used as catalyst components in the preparation of high-activity polyolefin catalysts, for which some sources mention oligomeric methylaluminoxanes (MAO) with R.dbd.CH.sub.3 as preferred. The degree of oligomerization n here plays an important role in the activity of the polyolefin catalysts, as was established by determination of the dependence of the catalyst activity on the average molecular weight of the aluminoxanes used (lit.: W. Kaminsky, Nachr. Chem. Tech. Lab. 29, 373-7 (1981); W. Kaminsky et al., Makromol. Chem., Macromol. Symp. 3, 377-87 (1986)).
The reaction of trialkylaluminums with water in inert hydrocarbons is mentioned in the literature as the known preparation process for alkylaluminoxanes. However, for the preparation of oligomeric methylaluminoxanes (MAO) from trimethylaluminum (TMA), other methods have also been mentioned as preferred, since it is known from the literature that the preparative method of slowly adding water to trimethylaluminum (TMA), described in more detail in, for example, U.S. Pat. No. 3,242,099, gives MAO only with difficulty and in very poor yield (EP-A-0 108 339); in addition, this method results in products which, in combination with the transition metal component, do not give high-activity catalyst systems (EP-B-0 069 951).
According to U.S. Pat. No. 4,924,018, an emulsion of from 0.5 to 10% of water in toluene is metered into a solution of trimethylaluminum, for example. The concentration of the resulting MAO solution and thus also the space-time yield are very low.
Furthermore, the addition of water to a solution of triisobutylaluminum (TIBA) (U.S. Pat. No. 4,772,736) in the shear field of a stirrer is described for a stirred reactor on a laboratory scale. The application of this process to a large industrial scale would be completely uneconomical, if not impossible, because of the disproportionately increasing stirring energy.